This invention relates to vibration suppression for tube and tube supports in large vapor generators. It particularly relates to a device for suppressing vibrations in spacer supports for the upper end of U-tubes in large steam generators used in pressurized water reactor nuclear power plants.
Large shell and tube type heat exchangers have been developed for generating pressurized vapor, by passing a heated fluid through the tubes to heat and vaporize a liquid that is circulated around the tubes. The tubes are provided as many layers of U-shaped tubes, the ends of which are attached to a tubesheet usually located at the shell lower end. Because the tubes are usually relatively long, the other or upper end of the tube legs is usually susceptible to flow-induced or mechanicall-induced vibrations, and tube spacer means have been provided between the tubes to control or eliminate such tube vibrations. However, it has been found that many pressurized water reactor nuclear power plants containing U-tube steam generators have tube vibration and wear problems involving the tube support diagonal spacer strips commonly called "batwings" used therein. These problems are caused by shell side flow-induced vibration of the batwings spacer strips. When stiffness of the batwing spacer strips is inadequate, the batwings vibrate under steam flow conditions, which causes excessive wear of tube walls and has a potential for failure of the batwing spacer supports. However, because access to the batwings within the steam generator is extremely limited, it is necessary to perform any repair operations from outside the vessel, in order to minimize exposure of personnel to radiation (ALARA) and also minimize expense of the repair.
The prior art has recognized problems of tube vibrations in heat exchangers and has provided some arrangements for stabilizing the vibration of such tubes in heat exchangers. For example, U.S. Pat. No. 3,400,758 to Lee discloses multiple parallel baffle means for sequentially supporting tubes in heat exchangers. U.S. Pat. No. 3,575,236 to Romanos discloses an anti-vibration tube spacer structure disposed between adjacent layers of U-shaped tubes in shell and tube type heat exchangers. U.S. Pat. No. 4,453,501 to Hayes et al discloses a means for testing from outside a vessel whether a heat exchanger tube is locked into a tube support. Also, U.S. Pat. No. 4,503,903 to Kramer discloses a tubesheet radial support device for heat exchangers. However, the known prior art has apparently not provided a mechanism and procedure for providing support for spacer strips located between tubes in vapor generators, particularly for supports adapted to be installed from outside the vessel.
Accordingly, a tube support vibration suppressor device has now been developed which can be installed and secured to the tube supports from outside the vapor generator vessel. The tube vibration suppressor device has adequate stiffness to stiffen the tube supports, such that vibrations and associated tube wear are reduced to acceptable low levels. The suppressor device is mechanically secured within the vessel, and its method of installation requires cutting two openings in the vessel shell and shroud at the proper opposite locations, inserting the vibration suppressor device parts through the openings, and then securing the parts in place between the adjacent tube spacer supports.